Particle Image Velocimetry Technology Research Articles

Shear failure analysis of slip zone soil with different coarse particle shapes: Visualized shear test and PIV technology

Coarse particle shape in slip zone soil influences the mesoscopic structure of the soil, which in turn affects soil shear strength and failure behavior. In order to investigate the effect of particle shape on the shear characteristics of coarse–fine-grained mixed slip zone soil, three types of coarse particles (spheroidal, rounded, and angular) were selected for mixing and matching, and a total of 10 sets of medium-scale shear tests were designed for this paper. To quantify the shear deformation and failure process of slip zone soils, particle image velocimetry (PIV) technology and the hanging hammer method were used to obtain mesoscopic data of the soil (displacement vector data of soil particles and elevation data of the shear failure surface), which were used to calculate shear band thickness, shear dilatation, and roughness coefficient of the shear failure surface. The results indicate that coarse particle shape can considerably affect the macroscopic mechanical properties (internal friction angle and shear strength) and mesoscopic deformation characteristics (shear band thickness, shear dilatation, and shear surface morphology) of soils. Angular coarse particles have higher interlocking strength than spheroidal and rounded coarse particles, allowing angular coarse-grained slip zone soils to develop large shear band thickness and rough shear failure surfaces. In addition, mesoscopic damage analysis suggests that the damage rate of slip zone soils decreases with increasing coarse particle shape complexity. These findings enhance comprehension of the failure characteristics of soil-rock mixture slopes and serve as a good reference for the stability analysis of similar slopes.

PIV Experimental Research and Numerical Simulation of the Pigging Process

The initial running speed of the pig during gas–liquid two-phase pipeline pigging can significantly influence the velocities of both gas and liquid phases within the pipeline. However, due to the complexity and limited understanding of these velocity variations, developing an effective operational plan for pigging becomes challenging. To enhance pigging efficiency and effectively seal the pig, it is crucial to monitor the velocity variations in the gas–liquid phase within the pipeline. In this study, an experimental platform was established to facilitate precise observation of these variations. Particle image velocimetry (PIV) technology was employed for a comprehensive understanding of gas–liquid two-phase velocities during pig operation in the pipeline. The experimental results demonstrated that increasing both the velocity and the initial liquid level height of the pig resulted in a corresponding augmentation of velocity fluctuation range. Specifically, at a holdup rate of 30%, there was a 10% reduction in the maximum liquid-phase velocity, while at a holdup rate of 25%, this reduction amounted to 16% compared to the pigging velocity.

Comparison of flow characteristics of plane jet impingement on a solid plate and on a sand bed

As compared to the well-researched case of a plane jet impinging on a solid plate, relatively rare attention was paid to the impingent on an erodible sand bed, which induces continuous bed transformations and interactively affects the jet development. The present study measured the flow of an impinging plane jet on a solid plate and on an erodible sand bed, respectively, by using particle image velocimetry technology, and then comparatively investigated the flow structure, main jet development and downstream wall jet development for the two cases. The results revealed that the jet impingement on the sand bed has a longer free jet region than that on the solid plate due to enlarged separation distance induced by localized scouring. The width of the plane jet impinging on the sand bed is larger than that on the plate by as high as five times the nozzle width, due to intensified interactions with the complex vortical structures in the concave scour hole. The impinging angle even decreases to negative values near the sand bed due to upward deflection of flow induced by bedform transformation. For both cases, however, the normalized streamwise mean velocity profiles exhibit universal self-similarity at different zones of jet development: specifically, the main jet and the wall jet satisfy exactly the same exponential function and the power law function, respectively.

Experimental study on multi-condition of axial flow pump in the whole flow field based on piv test

To study the internal flow characteristics of the axial flow pump in the whole flow field under different flow conditions, particle image velocimetry technology was used to measure the steady and unsteady flow fields of the axial flow pump, analyzed the velocity field distribution at the impeller inlet, impeller inner, guide vane inner, and guide vane outlet of the pump under different flow conditions (Q/Q des=0.8, 1, 1.1). Through the test and data analysis: under the three flow conditions, the velocity distribution trend of the impeller inlet of the axial flow pump is consistent and basically along the axis direction; there is a large velocity gradient in the flow field inside the impeller, and there is a significant acceleration near the hub trend, and there is a high-speed concentrated area; the velocity distribution trend in the guide vane is basically the same, and the fluid velocity changes more uniformly at the rated flow rate, and the flow tends to be more stable; a local high-speed area appears at the outer edge of the guide vane outlet, but in the second half The flow velocity in the pipeline is relatively uniform. The test results can provide a reference for the internal flow characteristics and performance optimization design of the axial flow pump.

The Influence of a Manifold Structure on the Measurement Results of a PIV Flowmeter

The application of particle image velocimetry (PIV) technology for monitoring natural gas flow is a new method of flow measurement. Since the principle of this technology was proposed, there are still some potential issues. This article investigates the influence of a manifold structure on the measurement results of a PIV flowmeter. A comparison is performed between concentric and eccentric manifold structures, using a circular straight pipe as reference, in terms of the measurement error of the PIV flowmeter and the internal flow state of the natural gas. The results demonstrate that the manifold structure significantly affects the measurement reliability of the PIV flowmeter, especially the eccentric manifold structure. Under flow conditions ranging from 100 to 600 m3/h, the maximum measurement errors caused by the concentric and eccentric manifold structures are 2.49% and 3.05%, respectively, which show a noticeable increase compared to the maximum measurement error of 2.08% observed for the circular straight pipe. Additionally, the influence of the manifold structure on the downstream flow field is also evident, as the eccentric manifold structure increases the turbulence intensity of the downstream fluid by nearly twofold. The addition of a rectifier can effectively improve the flow state and enhance the measurement reliability of the PIV flowmeter. For the concentric manifold structure under the condition of a 600 m3/h flow rate, the inclusion of a rectifier produces highly accurate measurement results, similar to those obtained by an ultrasonic flowmeter, with an error value close to zero. This study provides technical support for further promoting the practical application of PIV flowmeters.

Uplift behavior of nodular diaphragm wall: Experiment and theory

AbstractThe nodular diaphragm wall (NDW) is a novel foundation that can provide significant uplift load resistance compared to a typical diaphragm wall foundation. With the advantages of low noise, cost‐effectiveness, high work efficiency, and construction abilities close to existing buildings, NDW has excellent engineering application prospects in urbanization construction. However, the scarce knowledge on the uplift resistance, failure mode, and calculation method of the NDW has hindered its application in practice. In this paper, indoor model tests based on particle image velocimetry (PIV) technology are carried out to investigate the uplift behavior of three NDW models with different amounts and locations of nodular parts. The load transfer mechanisms of the three NDW models are discussed in detail, and special attention is given to the failure mode analysis. In addition, a theoretical analysis is implemented based on the load transfer approach. The transfer function and associated critical parameters are discussed in detail. Accordingly, an iterative procedure is proposed to interpret the load transfer information of an uplift NDW in multilayered soils under different loading levels. The findings derived in this paper are helpful to the uplift deformation, capacity calculation, and design of NDW in practical engineering.

Particle image velocimetry combining unsupervised learning and optical flow model

Particle Image Velocimetry (PIV) is a multi-point, transient, contactless flow field measurement technique which can obtain accurate data information for the flow field. Particle image velocimetry technology based on deep learning has been widely used, with higher measurement accuracy and testing efficiency than traditional algorithms. Algorithms based on supervised learning need real data for network training. However, obtaining real flow field data is difficult, so unsupervised learning methods are more suitable for network training. The LiteFlowNet3 network has only four layers of flow inference, leading to limited reconstruction accuracy, especially for complex flow field. This paper adds one layer of flow inference based on the original network, while increasing the last layer of the loss. The network is trained using an unsupervised learning method, focusing on improving reconstruction accuracy for real-flow field training. The experimental results show that the improved model can reduce the average endpoint error by up to 30.89 % and 13.33 % compared to the original model and the unsupervised LiteFlowNet. In addition, by building a two-dimensional PIV system to simulate the advection and vortex field, real particle image pairs were obtained and put into the trained model for testing, proving the feasibility for obtaining velocity fields in real flow field.

Mass transfer enhancement and hydrodynamic performance with wire mesh coupling solid particles in bubble column reactor

It is of vital significance to investigate mass transfer enhancements for chemical engineering processes. This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas–liquid mass transfer process in a bubble column. Particle image velocimetry (PIV) technology was employed to analyze the flow field and bubble motion behavior, and dynamic oxygen absorption technology was used to measure the gas–liquid volumetric mass transfer coefficient kLa. The effect of embedding wire mesh, adding solid particles, and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared. The results show that the gas–liquid interface area increases by 33% to 72% when using the wire mesh coupling solid particles strategy compared to the gas–liquid two-phase flow, which is superior to the other two strengthening methods. Compared with the system without reinforcement, kLa in the bubble column increased by 0.5–1.8 times with wire mesh coupling solid particles method, which is higher than the sum of kLa increases with inserting wire mesh and adding particles, and the coupling reinforcement mechanism for affecting gas–liquid mass transfer process was discussed to provide a new idea for enhancing gas–liquid mass transfer.

Experimental study of the Reynolds stress distribution and its self-similarity in a semi-confined impinging jet

This paper investigates the Reynolds stress distribution and its self-similarity of a semi-confined impinging jet using the two-dimensional particle image velocimetry (2D-PIV) technology. The confinement is achieved by placing a plate parallel to the impinging plate at the nozzle exit. Nine sets of measurements are conducted at three impingement distances (4, 5, and 6 times the nozzle diameter) and three Reynolds numbers (5084, 8179, and 13,926). The spatial distribution and the self-similarity of Reynolds stresses are obtained. The results indicate that high turbulence occurs mainly in the free jet shear layer and the wall jet shear layer. The variation of Reynolds stresses with impingement distances and Reynolds numbers are determined. The Reynolds stresses in the radial wall jet region do not exhibit self-similarity in the outer-scaled coordinates. Scaling parameters based on Reynolds stresses are proposed, and the Reynolds stress velocity scales decay by a power-law function in the self-similar region, while the Reynolds stress length scales increase linearly. The Reynolds stresses in the radial wall jet region show extremely strong self-similarity using the Reynolds stress scaling parameters normalization. Finally, the corresponding scaling laws for Reynolds stresses are obtained.

Experimental study on interaction between the internal solitary wave and a hydrofoil based on the spectral proper orthogonal decomposition

Internal solitary waves (ISWs) are a well-known phenomenon of water motion in the ocean, and their strong shear flow has a non-negligible harm to underwater marine engineering structures. To clarify the variation law of flow field and force during the interaction between ISW and common marine engineering structures-hydrofoils, in this paper, the spectral proper orthogonal decomposition (SPOD) method is introduced into the ISW problem for the first time. The advantage of this method is that it can display the flow field information in the frequency domain, and we obtained the flow field structure in the frequency domain during the whole flow process and mode 1 at the primary frequency with this method. We also obtained the time evolution flow field and force data through the particle image velocimetry technology and force sensor. The results show that the characteristics of flow field described by time domain and frequency domain show good consistency. According to the analyses results, we divide the flow process into low-frequency steady state and high-frequency disturbance. Most notably, we use the SPOD method to find that the sub-peak threshold of the flow frequency is surprisingly consistent with the sub-peak threshold of the force frequency. The main modes and frequency information of the flow field obtained by the SPOD method can provide valuable guidance for hydrofoil structures to avoid and predict ISW hazards in actual marine engineering operations.

An Improved Convolutional Neural Network for Particle Image Velocimetry

With the wide application of Particle Image Velocimetry (PIV) technology in various engineering and research fields, the requirements for the accuracy, computational efficiency, and robustness of PIV algorithms are increasing. Although traditional algorithms have wide applicability, they suffer from low accuracy, large computational cost, and poor robustness. Recently, deep learning algorithms have provided new solutions, especially, convolutional neural networks with different structures, which have achieved good performance on synthetic PIV datasets. This paper proposes a structural improvement scheme for PIV convolutional neural network models. Experiments verify that the proposed method can significantly optimize the performance of the model on synthetic PIV datasets, providing a novel approach for improving other convolutional neural networks for PIV analysis.

Pressure oscillation and vortex in an asymmetric T-junction

The T-junction structure with one inlet and two outlets is ubiquitous in natural and aerospace systems. However, previous research has mainly focused on vortex breakdown under steady-state flow in symmetrical structures. Limited research has been conducted on vortex breakdown in asymmetric structures, where the radii of the two channels differ. This creates a flow rate difference between the outlets, and the ratio of mass flow rate in the small channel to the large channel is defined as the splitting ratio. To study the appearance of vortex structures in the outlet channel under different flow rates and splitting ratios, a split-type asymmetrical circular cross-section pipeline experimental system that can be flexibly disassembled was designed and built. Pressure signals of each channel using pressure sensors were measured and analyzed. It is worth noting that a string tracing technology combined with particle image velocimetry (PIV) technology to monitor the outlet channel was adapted to visualize the flow. Results show that the pressure oscillations in the channels of the T-junction are related to the splitting ratio. Besides, asymmetric T-junction structure exhibits different large vortex structure formation and breakup processes in the two outlet channels, and these processes are influenced by the splitting ratio.

Pore‐scale simulation of the influence of temperature on particle motion based on LBM‐IBM‐DEM method

AbstractInvestigation on the depositional characteristics of suspended particles in porous media is crucial to prevent groundwater artificial recharge blockage. In this study, first, particle image velocimetry (PIV) technology was used to extract a 2D porous media skeleton structure formed by spherical superabsorbent resin particles. Second, based on the temperature influence analysis on the physical–chemical properties (including fluid viscosity, relative dielectric constant and zeta potential of solid surface), the Lattice Boltzmann Method‐Immersed Moving Boundary‐Discrete Element Method (LBM‐IBM‐DEM) coupling model was used to simulate suspended particle motion in porous media. The relationships between the suspended particle motion states, stable deposition forms, suspended particle spatial distribution and the collaborative influence of pressure difference, particle size and temperature are innovatively revealed. The results are as follows: (1) In the ‘first temperature effect range’, the suspended particles change in two states of detachment after adsorption and stable deposition. In the ‘second temperature effect range’, the suspended particles change in two states of stable deposition and migration. (2) The non‐uniformity of suspended particle spatial distribution in porous medium increases with the increasing of particle size and the decreasing of pressure difference. However, the temperature effect on suspended particle spatial distribution is weak. (3) Influence weights of pressure difference, particle size and temperature on the suspended particle motion are 2.92, 1.04 and 0.8, respectively.

Reinforcement effect and mechanism analysis of dredged sludge treated by alternating prefabricated radiant drain vacuum preloading method

The vacuum preloading method is widely applied in dredged sludge reinforcement, however, prefabricated vertical drain (PVD) clogging affects the effectiveness of ground reinforcement and leads to significant uneven settlement. To alleviate these deficiencies, this paper proposed an alternating prefabricated radiant drain vacuum preloading (APRD-VP) method considering the advantages of the alternating vacuum preloading (A-VP) method (delaying clogging) and prefabricated radiant drain vacuum preloading (PRD-VP) method (combining horizontal drainage and alleviating uneven settlement). The laboratory model experiments were conducted to explore the treatment effect of APRD-VP method, and the particle image velocimetry technology was employed to observe clogging range surrounding PVD. The experimental results demonstrate that APRD-VP method displayed a better reinforcement effect than the traditional method by analysis of water discharge, settlement, pore water pressure, water content, and vane shear strength. By investigating the clogging formation development for APRD-VP method, the maximum clogging range on both sides of the drainage board has been reduced by 3.15% and 14.02%. In addition, the empirical relationship between clogging range and settlement was established to can better judge and predict clogging range, which can lay the foundation for establishing the theory of computation of soft soil ground design suitable for APRD-VP method.

Study on the effect of internal reefs deflection on the flow field effect of unit reef

Artificial reef (AR) is generally utilized by the structure shape of unit reef (UR) in practical applications, and the UR construction part is the most important part to exert the flow field impact. However, there is currently limited scientific study on the effect of internal flow field effect inside the UR and lacks systematic theoretical basis. In this paper, the numerical simulation method was first verified by flume tank experiment with Particle Image Velocimetry (PIV) technology, and the results showed that numerical results were consistent with the experimental results. The numerical simulation method was then employed to assess the impact of the longitudinal interval on the flow field effect of three reef arrays, using the upwelling efficiency index as the evaluation standard. The study also investigated the influence of the deflection of individual reefs within the UR on the overall flow effect. The results indicate that the deflection of the reefs encountering the inflow initially had the most significant impact on the flow field. The flow field effect of the UR was optimal when the deflection angle was 30°, while the influence of deflection angle on the reefs at other positions was not significant. This study aimed to provide a reference for the layout design of UR.

Comprehensive investigations on flow field in liquid-solid mini-fluidized beds

The Particle Image Velocimetry (PIV) technology was adopted to study the expansion ratio, solid holdup, minimum fluidization velocity, velocity field, turbulent kinetic energy, vortex structure and particle velocity of liquid-solid mini-fluidized beds with bed diameter of 1–3 mm. Due to the wall effect caused by the decrease of bed diameter, the axial velocity at the central axis was 1.68–1.93 times of that near the wall. Both liquid and particle phases had tendency to move toward the central axis of bed. When the liquid velocity gradually increased, the turbulence phenomenon appeared in the liquid-solid mini-fluidized bed. Regarding particles, their axial velocity was mainly influenced by the superficial liquid velocity, while the radial velocity was predominantly by vortices and friction between particles. In this study, the overall movement of flow field was comprehensively obtained, which provided a certain theoretical reference for the design of the liquid-solid mini-fluidized bed reactors.

Influence of the co- and counter-swirl on combustion instability of the centrally staged combustor

The centrally staged combustor is an effective way to reduce NOx emissions from combustors. However, combustion instability caused by the mutual coupling between flames and acoustics during the combustion process is almost unavoidable. To better understand this problem, the effect of the swirl rotational direction is investigated in this paper using two different schemes with co-swirl and counter-swirl configurations. Pressure fluctuations and flame dynamics are investigated under self-excited combustion oscillation conditions. The CH* chemiluminescence distribution captured by a high-speed camera is utilized to characterize the flame macrostructure and heat release fluctuations. Furthermore, non-oscillating reaction velocity fields are acquired using particle image velocimetry (PIV) technology. The results indicate that the amplitude and frequency of the counter-swirl scheme are higher than those of the co-swirl scheme at varying main stage equivalence ratios. Combining the results from dynamic mode decomposition and the local Rayleigh index, it is found that the heat release regions of the counter-swirl scheme are mainly concentrated in the shear layer. Higher velocity gradients, vorticities, and strain rates in the inner shear layer (ISL) and outer shear layer (OSL) for the counter-swirl scheme are verified using PIV technology. The driving sources of thermoacoustic oscillations are located in the regions of the ISL, OSL, and the area where the flame impinges on the sidewall of the liner. Additionally, the counter-swirl scheme exhibits larger vorticities and strain rates in the ISL and OSL, facilitating the development of thermoacoustic oscillations.

Flow characteristics of a trapped-vortex pilot cavity under the influence of radial structure

In this study, using a laboratory-scale combustor model, we examined the flow modes in the trapped-vortex cavity under the influence of a radial bluff-body structure by particle image velocimetry (PIV) technology. The tested area included both inside the cavity and the mainstream zone. It is found that, under different inlet parameters, structure width, and circumferential positions, the flow characteristics change significantly for this structure. The number of vortexes, the distribution of vorticity, and the Q-value differ at different circumferential positions; while the increase in radial structure width, incoming flow velocity, and total pressure will all lead to stronger vortex flow. The flow pattern inside the cavity and behind the radial structure are coupled with each other, forming six typical flow modes. Further theoretical analysis summarized the causes of the six flow modes according to two aspects: how the mainstream influences the cavity flow, and the influence degree of the mainstream on the cavity flow. Considering the effect of the radial structure, the mainstream at different positions will have different effects on the cavity, which can be represented by the ratio of the radial position to the width of the structure. The influence degree was related to the inlet parameters and the width of the radial structure, which can be represented by the dynamic pressure of cavity inlet jets.

Experimental and Analytical Investigation of the Bearing Capacity of Bulbs for Squeezed Branch Piles

Reasonable estimation of the bearing capacity of bulbs is essential for the design of squeezed branch pile (SBP) foundations, and existing analytical methods cannot be applied to SBPs. This study investigated the bearing capacity of bulbs by model tests, field tests, and theoretical and numerical analysis. From the laboratory model loading test and transparent soil model test assisted by particle image velocimetry technology, the bearing features of SBPs and the displacement field around a bulb under failure state were investigated, respectively. It was found from the tests that the bulb’s bearing ratio is up to approximately 50% out of the total applied load to the pile at failure. Furthermore, by referring to Meyerhof’s theory of bearing capacity for deep foundations, an analytical method was proposed to calculate the bearing capacity of a bulb for an SBP considering its unique geometry. Finally, field tests with a real-size SBP and numerical study were conducted to verify the proposed method. The ultimate bearing capacity (UBC) of the bulb estimated by the proposed method has an acceptable difference of 4.21% from the model test and 17.6% from the numerical field cases. The proposed solution can be used as an effective explicit solution to evaluate the UBC of the single bulb of SBPs considering the pile’s dimensions and soil parameters.

Failure mechanism of single pile-friction footing hybrid foundation under combined V–H–M loadings by PIV experiments and FE method

The traditional monopile foundation is confronted with challenges in the context of the new generation of offshore wind turbines with greater power capacities. On this basis, the single pile-friction footing hybrid foundation is investigated, whose bearing capacity is largely improved by combining a circular friction footing at the mudline. This paper discusses the failure mechanisms and bearing capacities of this hybrid foundation in sand under combined vertical-horizontal-moment (V–H-M) loadings by laboratory experiments and the finite element method. By adopting Particle Image Velocimetry (PIV) technology in model tests, failure mechanisms of a single pile and the hybrid system are compared. The results show that the cavitation and compaction phenomenon can be captured in the depth range of 0–0.7 pile embedment depth) for the hybrid foundation. Also, due to the settlement of the footing, a deformation area with a concave area and a small peak value can be found under the footing, which is quite different from that of the pile under V–H-M combined loadings. Intensive parametric studies were performed through FE method, and the results indicate that increasing the footing diameter has a more pronounced effect on the bearing capacity compared to that of increasing the length-diameter ratio of the pile.